The present invention involves a monitoring system which is responsive to the angular velocity condition of a rotating member of a machine.
One area where such a monitoring system is particularly useful is in agricultural machines, such as seed planters and combines, which may have one or more shafts whose continued rotation at a specific speed or within a range of speeds is essential to the proper operation and longevity of the machine.
The approaches certain others have taken to monitor the angular velocity of a shaft are shown in U.S. Pat. Nos. 3,611,343 to Schoenbach; 3,739,367 to Fathauer; and 3,921,159 to Steffen. A feature common to the disclosures of these three patents is the provision of a magnetically operable reed switch in proximity with the rotating shaft, and a permanent magnet mounted on the shaft such that the reed switch is actuated by the magnet on each revolution of the shaft. The reed switch, connected to an electrical current source, provides a pulsed DC electrical signal in which the frequency and duration of the pulse varies in accordance with the opening and closing of the reed switch as the shaft rotates. Electrical circuitry is provided to compare the frequency or duration of the signal pulses from the reed switch with a selected frequency or duration which corresponds to a desired shaft rotational speed. Deviation from the desired frequency or duration results in activation of an alarm to indicate to the machine operator that an undesirable shaft speed condition is present.